1. Field of the Invention
The invention relates to host based storage subsystem management and in particular to a method and associated apparatus for storage of configuration information, shared among a plurality of attached host systems, on a reserved area of a commonly attached storage subsystem.
2. Description of Related Art
It is common in the art relating to storage subsystems that host system programs are, in part, responsible for administration and management of attached storage subsystems. For example, initial configuration of a storage subsystem to allocate available storage capacity to the storage of data may be performed by such a host program. The host program, for example, interacts with an administrative user to determine the desired configuration of the storage space and then transmits any requisite command sequences to the storage subsystem to effectuate the desired configuration. The configuration thereby become known to the host system as well as the attached storage subsystem.
Further, it is known in the art to permit a plurality of host systems to share access to common storage subsystems. In such clustered environments where a plurality of hosts connect to a common storage subsystem, the plurality of hosts communicate their respective configuration and management operations among one another. When a first host system configures, re-configures, or otherwise administers an attached storage subsystem, other host systems attached to that storage subsystem need to be informed of any changes in the configuration or operation of the storage subsystem.
As taught by prior techniques, host systems attached to a common storage subsystem have used a communication channel such as a local area network (LAN) or other communication channel to exchange such administrative messages. Each host system broadcasts messages on the communication channel to other host system to announce the configuration or other administrative operations performed by the broadcasting system. A number of the host systems (frequently all) maintain a store of the current configuration information related to the present state of the storage subsystem. As messages are received from other host systems, each host system updates its model of the present storage subsystem configuration.
These methods and structure taught by prior techniques create a problem for a host system which is newly attached to a common storage subsystem or which is temporarily disconnected from the other host systems. Such a system must seek to synchronize its model of the present state of the storage subsystem by inquiring of one or more of the other systems as to the present status of the storage subsystem. When so inquiring to synchronize status, a host system must determine whether any received status information is more recent than status already known to the host system.
It is therefore a problem to devise a simple method and associated apparatus to permit a plurality of host systems to maintain synchronization regarding state information pertaining to a commonly attached storage subsystem.